Pitting corrosion silver

Fig. 9. Corrosion model of silver development. As the haUde ion, X, is removed into solution at the etch pit, the silver ion,, travels interstitiaHy, Ag/ to the site of the latent image where it is converted to silver metal by reaction with the color developer, Dev. Dev represents oxidized developer.

Most simple inorganic salt solutions cause virtually no attack on aluminium-base alloys, unless they possess the qualities required for pitting corrosion, which have been considered previously, or hydrolyse in solution to give acid or alkaline reactions, as do, for example, aluminium, ferric and zinc chlorides. With salts of heavy metals —notably copper, silver, and gold —the heavy metal deposits on to the aluminium, where it subsequently causes serious bimetallic corrosion. 

Aluminum Foil. Studies of various foods wrapped in aluminum foil show that food products to which aluminum offers only fair resistance cause little or no corrosion when the foil is in contact with a nonmetallic object (glass, plastic, ceramic, etc.) The reactions, when found, are essentially chemical, and the effect on the foil is insignificant. However, when the same foods are wrapped or covered with foil that is in contact with another metallic object (steel, tinplate, silver, etc.), an electrochemical or galvanic reaction occurs with aluminum acting as the sacrificial anode. In such cases, there is pitting corrosion of the foil, and the severity of the attack depends primarily on the food composition and the exposure time and temperature. Results obtained with various foods cov-... 

Cyanides such as silver cyanide AgCN, copper cyanide Cu(CN)2, and gold cyanide AuCN, that are used in galvanoplastic processes, lead to pitting corrosion of aluminium due to the presence of cations of heavy metals (silver, copper, and gold). 

Material Acid droplet pitting, nylon hose destruction Rubber cracking, silver tarnishing, paint blackening Corrosion, soiling, materials deterioration... 

The pits are generally embossed into the substrate (polycarbonate or polymethylmethacrylate) layer by an injection-molding process, and are used to indicate whether a data bit is 0 or 1. An aluminum or silver layer provides a reflective surface, and is protected from corrosion and damage by a radiation-cured acrylate (lacquer) layer, onto which a label is usually printed.197... 

Nickel is outstandingly resistant to hot or cold alkalies. Only silver and possibly zirconium are more resistant. Nickel exposed to boiling 50% NaOH corrodes at the rate of 0.06 gmd (0.0001 ipy). It also resists fused NaOH, low-carbon nickel being preferred for this application in order to avoid intergranular attack of the stressed metal stress relief anneal, 5 min at SJ5°C (llOO F) is advisable. Nickel is attacked by aerated aqueous ammonia solutions, a soluble complex, Ni(NH3)i+, forming as a corrosion product. It is also attacked by strong hypochlorite solutions with formation of pits. 

An IPEN rack containing 1060, 6061 and 6262 alloys, used in fuel assembly manufacture, was also immersed in the basin. After 16 months of exposure, it was observed that some pitting had occurred on the uncoupled coupons, mostly on the top surfaces. The aluminium couples were stained inside the crevices but were not pitted. The stainless steel-aluminium galvanic coupons were much more severely corroded. Additional laboratory tests were conducted to determine whether increased levels of silver in the basin water could have increased the corrosion of the aluminium cladding in the IPEN basin. Results indicated no pitting but an increase in darkness of the surface oxide colour with the increase of silver concentration. 

Kane, R. D., Wilhelm, S. M., and McIntyre, D. R., Application of the Critical Pitting Temperature Test to the Evaluation of Duplex Stainless Steel, Corrosion Testing and Evaluation Silver Anniversary Volume. ASTM STP 1000, R. Baboian and S. W. Dean, Eds., ASTM International, West Conshohocken, PA, 1990, pp. 289-302. 

Figure 6.8 Water freely flowing out of a silver-plated water jug with pit through corrosion.

Figure 9.50 Close-up of corrosion pits in a water jug (Fig. 6.8) made of a silver-plated zinc casting.

SILVER COMPOUNDS. In laboratory tests, solutions of silver compounds were corrosive to all aluminum alloys causing localized pitting attack. See also Ref (Dp. 142, (3) p. 73. 

Localized corrosion is not always related to aggressive anions. Pits may form on metal surfaces due to imperfect passivation. This may be a consequence of a poor film quality or the action of metallic inclusions. Two examples have been already mentioned in Chapter 5. One example is the localized corrosion of silver at potentials corresponding to early film formation (Chapter 5), another one is the effect of Cu inclusions on passivity breakdown of Al (Chapter 5). 

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